The present invention relates generally methods of packaging electronic components. More particularly, the present invention relates to a method of forming packaged electronic components with reduced thickness.
Virtually every business in the world has become dependent, directly or indirectly, on electronic components such as integrated circuits. In addition, electronic components have permeated our personal lives through their use in systems that control or contribute to almost every aspect of our day from coffee making to network computing. This application of electronic components to what were once seemingly unrelated fields has created a huge demand for these components in increasingly diverse industries and locations. Consequently, there has been a corresponding increase in demand for better methods and structures to package electronic components and for smaller packaged electronic components. This demand has made electronic component packaging one of the most critical and competitive markets in the electronics industry.
To stay competitive, those of skill in the art of electronic component packaging are constantly seeking better ways to provide protection of the extremely fragile electronic components from environmental elements and contamination while, at the same time, providing a solution that does not significantly increase the size or the cost of the finished, packaged electronic component.
FIG. 1 is an enlarged cross-sectional view of an exemplary prior art packaged electronic component 10. As shown in FIG. 1, a first surface 32 of an electronic component such as an integrated circuit (IC) chip 30 was typically mounted to a first surface 18 of prior art substrate 13 by a layer of adhesive 31 so that IC chip 30 was positioned above prior art substrate 13. IC chip 30 was typically mounted to prior art substrate 13 in a location central to metallizations 22. Also shown are bonding pads 38 that were located on a second surface 36 of IC chip 30. Bonding pads 38 were typically electrically connected to corresponding contacts 23 by bond wires 40, made of gold or aluminum for example, using conventional wire bonding techniques. Contacts 23 were connected to metallizations 22. Electrically conductive vias 14 electrically coupled metallizations 22 on first surface 18 of prior art substrate 13 to metallizations 26 on second surface 20 of prior art substrate 13.
Also shown in FIG. 1, is layer of encapsulant 42 that was applied over the entire assembly. In particular, layer of encapsulant 42 covered IC chip 30 including bonding pads 38, bond wires 40, contacts 23, metallizations 22 and the remaining exposed first surface 18 of prior art substrate 13.
As also shown in FIG. 1, interconnection balls 28, typically eutectic solder balls, were attached to contacts 27 using conventional techniques. Contacts 27 were, in turn coupled to metallizations 26 on second surface 20 of prior art substrate 13. Interconnection balls 28 were often arranged in an array thus forming a ball grid array.
As can be seen in FIG. 1, the resulting prior art packed electronic device 10 had a thickness 60 extending from top surface 48 of encapsulant 42 to bottom surface 39 of prior art substrate 13. In prior art packaged electronic devices, such as prior art packaged electronic device 10, the value for thickness 60 was relatively large and typically on the order of 1.1 to 2.0 millimeters. This was highly disadvantageous because the relatively large thickness 60 meant larger and thicker systems. In a market that increasingly stresses small size and portability, this situation was far from ideal.
One major reason that prior art packaged electronic device 10 had a relatively large thickness 60 was the additional thickness 70 that prior art substrate 13 added to prior art packaged electronic device 10. Prior art substrate 13 was necessary to allow electrical connections to be made between IC chip 30 and off chip locations by way of contacts 23, metallizations 22, electrically conductive vias 14, metallizations 26, and contacts 27, as discussed above. Thickness 70 was added to prior art packaged electronic device 10 because, in the prior art, IC chip 30 was mounted on top of prior art substrate 13, to first surface 18 of prior art substrate 13. Consequently both the thickness of IC chip 30 and the thickness 70 of prior art substrate contributed to the thickness 60 prior art packaged electronic device 10. This added thickness was considered a necessary evil in the prior art because it was thought that the IC chip 30 needed to be mounted on top of prior art substrate 13 to provide a strong and stable structure during die electrical connection and to stabilize IC chip 30 within the structure of prior art packaged electronic device 10.
In addition to being relatively thick and cumbersome, prior art packages, such as that shown in FIG. 1, were particularly ill suited for newer electronic devices such as image sensor die and other optical devices, which not only require small size, i.e., minimal thickness, but also require mounting of optical elements such as glass plates or lenses. Image sensors and assemblies are well known to those of skill in the art. Image sensors typically include an active area, which is responsive to electromagnetic radiation. In prior art image sensor assemblies, an image sensor was located within a housing that supported a window. Radiation passed through the window and struck the active area of the image sensor, which responded to the radiation. For the image sensor to function properly, the image sensor had to be positionally aligned with the window to within tight tolerances.
Since prior art packages, such as shown in FIG. 1, were not well suited to packaging image sensor dice, in the prior art, an image sensor assembly was formed by mounting the image sensor directly to a printed circuit motherboard. After the image sensor was mounted, a housing was mounted around the image sensor and to the printed circuit motherboard. This housing provided a seal around the image sensor, while at the same time, supported a window above the image sensor.
Beaman et al., U.S. Pat. No. 5,821,532, hereinafter Beaman, which is herein incorporated by reference in its entirety, is one example of a prior art image sensor assembly. Beaman sets forth a printed circuit board that included a pair of apertures used as alignment features for mounting the image sensor and for mounting the optics that included the window. More particularly, the pair of apertures were used as the mounting reference for the image sensor and then were used as the mounting reference for the optics.
As discussed in Beaman, prior art image sensor assemblies used a housing to support the window and to hermetically seal the image sensor (see housing 24 and window 25 of Beaman FIG. 4 for example). This housing was typically formed of ceramic that advantageously had excellent resistance to moisture transmission to protect the image sensor from the ambient environment. In addition, ceramic housings provided the strength and stability thought necessary in the prior art. However, ceramic is relatively expensive and heavy compared to other packaging materials and, in the current market, it is critical to form the image sensor assembly at minimal cost. In addition, and perhaps even more disadvantageous, was the fact that prior art image sensor assemblies were very large and bulky and further added to the thickness and overall size of subsystems employing these prior art image sensor assemblies.
In addition, mounting the housing at the printed circuit board level, as was done in the prior art, was inherently labor intensive and made repair or replacement of the image sensor difficult. In particular, removal of the housing exposed the image sensor to the ambient environment. Since the image sensor was sensitive to dust, as well as other environmental factors, mounting the housing at the printed circuit board level made it mandatory to make repairs, or to replace, the image sensor in a controlled environment such as a clean room, otherwise there was a risk of damaging or destroying the image sensor. Thus, using the prior art method of mounting the housing at the printed circuit board level often meant transporting the entire motherboard into the clean room.
What is needed is a method for packaging an electronic device, which results in a thinner packaged device and can be used to package image sensor devices.
In accordance with the present invention, an electronic device is packaged by first forming a hole through a substrate, from a fist surface of the substrate to a second surface of the substrate. According to the invention, the hole is made large enough to position the entire electronic device within the hole. A tape is then applied to the second surface of the substrate to cover a second side of the hole, thereby creating a tape surface at the bottom of the hole. The electronic device is then positioned within the hole such that a second surface of the electronic device is in contact with, and adhered to, the tape surface at the bottom of the hole. Consequently, using the method of the invention, the tape provides the stability for the electronic device, such as an IC, during die attachment, but the tape, unlike prior art structures, does not add significantly to the thickness of the package.
Once the electronic device is positioned at the bottom of the hole and adhered to the tape surface at the bottom of the hole, electronic connections are made between the electronic device and the substrate using known methods such as bond wires. With the electronic connections made, a layer of encapsulant is applied to a first surface of the electronic device, a first surface of the substrate, the electronic connections, e.g., the bond wires, and to fill in any gaps between the electronic device and the sides of the hole. Consequently, using the method of the invention, the encapsulant provides the stability for the packaged electronic device however, unlike prior art structures, the encapsulant does not add significantly to the thickness of the package.
The method of the present invention is particularly well suited to packaging sensor devices such as sensor dice. In this embodiment, a glass plate or lens is placed over the active surface of the sensor die to cover a first region of the first surface of the sensor die, before the encapsulant is applied. Then, the encapsulant is applied to: the first surface of the substrate; the portion of the first surface of the sensor die not covered by the optical element; the electronic connections, e.g., the bond wires; and to fill in any gaps between the sensor die and the sides of the hole. In this embodiment of the invention, the encapsulant does not cover a first surface of the optical element, however, the encapsulant covers the sides of the optical element and serves to surround and hold the optical element in place over the active region of the sensor die.
In one embodiment of the invention, several electronic devices are packaged at once by providing a large, multi-package substrate and forming a matrix of multiple holes in the multi-package substrate. The multiple holes are cut through the multi-package substrate, from a fist surface of the multi-package substrate to a second surface of the multi-package substrate. According to the invention, the holes are made large enough to position an entire electronic device within each hole. A tape is then applied to the second surface of the multi-package substrate to cover a second side of each hole, thereby creating a tape surface at the bottom of each hole. Electronic devices are then positioned, one electronic device within a corresponding hole such that a second surface of each electronic device is in contact with, and adhered to, the tape surface at the bottom of its corresponding hole.
Once the electronic devices are positioned at the bottom of their corresponding holes and adhered to the tape surface at the bottom of their corresponding holes, electronic connections are made between the electronic devices and the multi-package substrate using known methods such as bond wires. With the electronic connections made, a layer of encapsulant is applied to a first surface of the electronic devices, a first surface of the multi-package substrate, the electronic connections, e.g., the bond wires, and to fill in any gaps between the electronic devices and the sides of their corresponding holes. The encapsulant is then dried or cured and the individual electronic devices are then singulated by methods well known to those of skill in the art.
The method of the present invention is particularly well suited to packaging multiple sensor devices such as sensor dice. In this embodiment, the electronic devices are sensor dice and a glass plate or lens is placed over the active surface of each sensor die to cover a first region of the first surface of each sensor die, before the encapsulant is applied. Then, the encapsulant is applied to: the first surface of the multi-package substrate; the portions of the first surface of the sensor dice not covered by the optical elements; the electronic connections, e.g., the bond wires; and to fill in any gaps between the sensor dice and the sides of their corresponding holes. In this embodiment of the invention, the encapsulant does not cover a first surface of the optical elements, however, the encapsulant covers the sides of the optical elements and serves to surround and hold the optical elements in place over the active regions of the sensor dice. The encapsulant is then dried or cured and the individual packaged sensor dice are then singulated using methods well known to those of skill in the art.
Using the method of the invention, packaged electronic devices are provided which are thinner, require less materials, are less expensive, and can be manufactured using industry standard materials and equipment. In particular, according to the invention, the electronic device is situated within the substrate. Therefore, in contrast to the prior art, the packaged electronic devices made according to the method the invention are thinner because the thickness of the substrate is not added to the thickness of the electronic device.
In addition, according to the invention, the electronic device is held in position by the tape surface at the bottom of the hole and then by the encapsulant surrounding, and covering, at least a portion, of the electronic device. Consequently, and in contrast to the prior art, the packaged electronic devices of the invention do not require expensive adhesives, the labor, or step, to apply these adhesives or the added thickness of these adhesives.
In addition, when the method of the invention is used to package sensor devices, such as sensor die, the package is not only thinner and protected from the elements, but the optical element is held in position by the adhesive. Consequently, and in contrast to the prior art, there is no need for a sensor housing mounted around the sensor die and to the printed circuit motherboard. Therefore, using the invention, the sensor dice can be packaged more cheaply than prior art devices and, in contrast to prior art systems, the senor dice can be serviced and replaced in the field. The resulting packaged sensor die is also smaller, thinner, lighter, and less expensive to produce than prior art sensor die systems.
These and other features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.